Foreman Maintain

Currently it is possible to run incremental backup specifying a previous backup directory without actual backup files, e.g.:

~]# foreman-maintain backup online --incremental /tmp /tmp

^ finishes successfully even if /tmp contains no backup files, command produces full backup. The only condition is that that the previous dir has to exist. This way, user could unknowingly create full backups instead of incremental. I'd suggest either to make f-m fail with error in such case, or proceed with message warning user (something like "Did not find backup files in previous backup directory, proceeding with full backup")